Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$132.60	6.124%	$140.7204	$140.72	$140.70	$140.70
Purchase #2	$78.25	5.420%	$82.4912	$82.49	$82.50	$82.50
Purchase #3	$21.86	7.376%	$23.4724	$23.47	$23.45	$23.50
Purchase #4	$74.33	10.724%	$82.3011	$82.30	$82.30	$82.30
Purchase #5	$88.30	12.255%	$99.1212	$99.12	$99.10	$99.10
Purchase #6	$228.56	4.532%	$238.9183	$238.92	$238.90	$238.90
Purchase #7	$10.77	5.302%	$11.341	$11.34	$11.35	$11.30
7 purchase totals =	$634.67		$678.3656	$678.36	$678.30	$678.30